Some vehicles are designed to use electricity as the source of power for propulsion. Such vehicles have an energy storage for holding the electric power, and such storage can be in form of a battery pack configured to be mounted on the vehicle. The battery pack has an electric connection to the vehicle, allowing the vehicle's propulsion motor or other drive unit to draw electric energy from the battery. In some situations the vehicle can feed electric energy back into the battery pack, for example during so-called regenerative braking.
Many battery packs are configured so that they can be recharged with electric energy as needed. Some vehicles have an external charge port for connecting an external energy source and thereby recharging the battery, and others may charge the battery via an onboard combustion engine. Another way to achieve energy replenishment is to exchange the current battery pack for a fully charged one. This technique can also be used when the old battery pack is in need of service, so as to allow the vehicle to continue driving.